Veldhuis, M. P. et al. (2019) Cross-boundary human impacts compromise the Serengeti-Mara ecosystem. Science, 363(6434), pp. 1424-1428. (doi:10.1126/science.aav0564). This is the author’s final accepted version. There may be differences between this version and the published version. You are advised to consult the publisher’s version if you wish to cite from it.

http://eprints.gla.ac.uk/183914/

Deposited on: 19 July 2019

Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk

1

Title: The Serengeti squeeze: cross-boundary human impacts compromise an

iconic protected ecosystem

Authors: Michiel P. Veldhuis1*, Mark E. Ritchie2, Joseph O. Ogutu3, Thomas A. Morrison4,

Colin M. Beale5, Anna B. Estes6,7, William Mwakilema8, Gordon O. Ojwang1,9, Catherine L.

Parr 10,11,12, James Probert10, Patrick W. Wargute9, J. Grant C. Hopcraft4 and Han Olff1

Affiliations:

1University of Groningen, Nijenborg 7, 9747AG Groningen, The Netherlands

2Syracuse University, 107 College Place, Syracuse, NY 13244, USA

3University of Hohenheim, Fruwirthstrasse 23, 70599 Stuttgart, Germany

4University of Glasgow, Glasgow, G128QQ, United Kingdom

5University of York, York YO10 5DD, United Kingdom

6Pennsylvania State University, University Park, PA 16802, USA

7The Nelson Mandela African Institution of Science and Technology, Arusha, Tanzania

8Tanzania National Parks, Arusha, Tanzania

9Directorate of Resource Surveys and Remote Sensing, P.O Box 47146 - 00100, Nairobi, Kenya

10University of Liverpool, Liverpool, L69 3GO, United Kingdom

11University of the Witwatersrand, Wits 2050, Johannesburg, South Africa

12University of Pretoria, Pretoria 0002, South Africa

*Correspondence to: m.p.veldhuis@gmail.com

Abstract: Protected areas provide major benefits for humans in the form of ecosystem services,

but landscape degradation by human activity at their edges may compromise their ecological

functioning. Using multiple lines of evidence from 40 years of research in the Serengeti-Mara

ecosystem, we find that such edge degradation has effectively “squeezed” wildlife into the core

protected area and has altered the ecosystem’s dynamics even within this 40,000 km² ecosystem.

This spatial cascade reduced resilience in the core and was mediated by the movement of grazers

which reduced grass fuel and fires, weakened capacity of soils to sequester nutrients and carbon,

and decreased responsiveness of primary production to rainfall. Similar effects in other protected

ecosystems worldwide may require rethinking of natural resource management outside protected

areas.

One Sentence Summary: Anthropogenic impacts at the edges of an ecosystem change the

ecological functionality at the core

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Main Text: Biodiversity is critical for sustaining ecosystem services (1–4), yet the major

challenge is how to conserve it. Protected areas (PAs), in which human activities such as

hunting, grazing, logging or conversion to cropland are restricted represent the dominant

conservation strategy worldwide (5), despite potential conflicts of interest with historic rights or

well-being of indigenous people (6). However, the sustainability of the PA strategy to preserve

biodiversity and ecosystem services is uncertain. One third of PAs are under intense human

pressure globally (7), especially from anthropogenic activities along their borders and despite

heavy protection (8–11). A major question is how these edge areas can be managed most

effectively to best preserve both biodiversity and human livelihoods (12). Previous studies

suggest that both the rate of landuse change and the growth of human populations can be fastest

near protected area boundaries (13–16), which accelerate the rate of edge degradation through

increased livestock production, crop cultivation, and extraction of natural resources such as

charcoal and bushmeat. In regions with high human density, the sharp contrast in natural

resources across PA boundaries leads to “hard edges” which exacerbates human-wildlife

conflicts (17), leading to two opposing intervention strategies. Fencing PAs as a form of “land

sparing” from intensively used surrounding areas can solve some human-wildlife conflicts but

also prevents beneficial temporary use of areas outside the reserve by wildlife, and requires

intensive management that can be too costly for large reserves in developing countries (18–20).

An alternative strategy involves “land sharing”, which promotes the coexistence of humans and

wildlife, especially in buffer zones (21). The majority of the earth’s PAs are not fenced,

questioning if anthropogenic activities at the edges are increasingly compromising the ecological

processes in the core. The objective of our research is to assess if edge effects are currently

undermining the ecological integrity that PAs aim to protect.

The concept of spatial compression in Pas (Fig.1)

At low human population density, people can extract sufficient resources and receive additional

benefits from Pas without compromising them and conversely PAs can profit from the presence

of people. Under these conditions, livestock and wildlife can coexist outside core protected areas

(CPAs; 22, 23). Unprotected areas (UPAs) can support ecotourism and harvesting of wildlife,

while livestock keeping can create local nutrient hotspots that increase biodiversity (24, 25). This

can lead to mutually beneficial relationships between people and wildlife (26) over longs periods

of time (27). However, steep increases in human populations (through population growth and/or

migration towards CPAs) can result in unsustainable use and thus reduce wildlife populations

both outside and along the edges of the CPAs (28–30). This may impose a form of habitat

compression that increases wildlife densities within the CPAs by making their effective size

smaller than their geographic size. Such habitat compression may result in apparently positive

effects (e.g. increased wildlife densities) becoming negative in the long-term if they cause

undesirable changes in the functioning and stability of the ecosystem.

Here, we show how spatial compression alters the key ecological functioning of the Serengeti-

Mara ecosystem in Tanzania and Kenya, one of the largest, most iconic PAs in the world. This

ecosystem is famous for its soft-edge land-sharing conservation strategies that buffer the CPAs

formed by the Serengeti National Park (SNP), the Mara Reserve and several adjacent areas with

similar and complementary management to the national parks (CPA: IUCN-cat. II, see (31),

Table S1). The ecosystem is managed to protect the diversity of wildlife and ecological

processes, foremost the migration of over 2 million large herbivores, primarily wildebeest

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(Connochaetes taurinus), zebras (Equus quagga) and Thomson’s gazelles (Eudorcas thomsonii)

(32). The spatial layout of a set of protected areas with different management supports this

migration (Fig. S1) by allowing animals free access to spatio-temporally variable forage within

the CPA, adjacent PAs with Sustainable Resource Use (PASRU: IUCN-cat. V and VI) and

UPAs. Using a combination of long-term field experiments, census data and remote sensing, we

show that increasing human populations, and their accompanying livestock and land conversion

practices, have “squeezed” the (migratory) grazing animals into an increasingly smaller part of

the CPA. We provide evidence that compression of wildlife has resulted in increased grazing

intensity in the CPA that decreases rangeland productivity, changes fire regimes, reduces soil

carbon storage and alters seasonal water retention. Our study demonstrates how land use at the

borders of a large PA modifies wildlife-vegetation interactions within and consequently changes

multiple ecosystem processes and services in the CPA.

Increased human dominance outside the CPA

From 1999 to 2012, the human population in the areas surrounding Serengeti-Mara increased by

2.4% per year on average (Fig. S2-S6; (31)). The human population growth rate was higher in

the UPA along the western boundaries, inhabited by Sukuma and Kuria agro-pastoralists,

compared with the PASRU along the eastern boundaries of the CPA where Maasai pastoralists

herd their livestock. Concomitantly, crop agriculture expanded from 37.0% of the region in 1984

to 54.0% in 2018 (Fig. S7; Table S2-S3; (31)). The growth of the cattle population (0.9% on

average per year, 2002-2012) was especially high in the wetter Tanzanian Mara Region, towards

Lake Victoria (4.2% per year), despite there being very little land outside the CPA left for

grazing in this area. Sheep and goat populations increased steeply in all the regions bordering the

CPA (3.8% per year; Fig. S8; (31)). Concurrently, grazing lands exhibited intensifying impacts

as evidenced by decreasing herbaceous vegetation green up, most notably in the PASRU, (Fig.

S9-S11; (31)) and virtually no fires outside the CPA since 2005 (Fig. 2, S12-S14; (31)).

Expanding edge effects induce spatial compression

We use unique and detailed data from the Narok subarea of the ecosystem to show how livestock

densities increased not only close to the border but also within the CPA over the past four

decades, likely displacing wild herbivores into the SNP and leading to declining densities in

MMNR (Fig. 3, S15-S19, Tables S4-S6; (31)). Here, human settlement and population densities

have increased enormously, especially close to the CPA boundary (note that increased people

densities inside the MMNR in Fig. 3 represent park and lodge staff, not movement of local

people living outside the reserve). The wildlife biomass inside the first 15km of the CPA reduced

by 75% in the wet season and by 50% in the dry season from the 1970s to 2000s. The latter

declines are largely due to changes in the abundance of the Loita sub-population of migratory

wildebeest and zebra that traditionally use the MMNR as their dry season range. Although such

detailed data are not available for the rest of the ecosystem, several indicators show that this

spatial compression phenomenon happened throughout the ecosystem.

In recent years, Maasai pastoralists in the PASRU have moved their bomas towards the borders

of the CPA (Fig. S20-S25; (31)) and even established bomas up to 10 km inside the CPA (Fig.

2). In addition, Maasi pastoralists with bomas outside the CPA might bring their herds on illegal

multi-day grazing trips into the CPA, as opposed to short, nightly grazing trips by the agro-

pastoralists on the west. The trend to push more livestock further into the CPA is probably in

4

response to declines in palatable forage in the remaining communal village grazing lands (30,

33).

The resulting cross-boundary human pressures also affect the extent of the migratory movements

of large herbivores, a defining ecological process of the Serengeti-Mara ecosystem. Ecosystem-

wide movement data obtained by GPS collaring of migratory wildebeest show avoidance of the

CPA margins in the last two decades and use has especially decreased along the borders of

PASRU and concentrated at the core (Fig. 4A-B, S26; (31)). Three lines of evidence suggest that

these patterns are best explained by increased competition between migratory wildebeest and

livestock.

First, the analysis of boundaries with UPAs where patrolling is medium (Fig. S1; (31)), such as

the border of Maswa Game Reserve, indicates that agro-pastoralists enter the park with their

livestock on a daily basis, producing an extensive network of livestock paths (Fig. 2, S22-S23,

S27; (31)). This coincides with a strong reduction in maximum vegetation greenness (maxNDVI)

within the first 7 km inside the CPA (>10%; Fig. 4G-H), as well as a significant decline in the

area of the CPA burned in the past 16 years from 52% to 29% corresponding to 3184 km² in total

(GLM: F1,14=-5.9, p < 0.05; Fig. 4E-F). The most severe changes in maxNDVI and fire coincide

with a high density of livestock paths and (temporary) livestock corrals (bomas), suggesting

illegal livestock incursions into the protected area removes vegetation biomass (Fig. 2, S10, S13;

(31)).

Second, these effects are ameliorated in areas with increased border control where illegal grazing

is more effectively excluded. The boundaries of the UPAs with strong border control, such as the

edges of the Grumeti Game Reserve, show less drastic changes in NDVI (Fig. 4, compare UPA

Strong with UPA Medium), suggesting these areas are less intensively grazed by livestock.

Along UPA Strong boundaries, wildebeest increased their use close to the border, whereas in the

UPA Medium areas wildebeest use increased beginning at 7 km inside the border, corresponding

to the distance of livestock incursions.

The third line of evidence suggesting livestock compete with wildlife comes from observing the

response of wildebeest in the different PASRU boundaries (Fig. 4C-D, S26; (31)). In Narok

where the intensity of use by wildebeest utilization was previously highest, wildebeest utilization

has declined up to 15 km inside the CPA, while along the border with Loliondo Game Controlled

Area (LGCA) the decreased use only stretches a few kilometers inside. Most notably, utilization

in the Ngorongoro Conservation Area (NCA) increased in recent years. There are multiple

explanations for these contrasting effects between the different PASRU. First, NCA has lower

human and livestock population densities than in LGCA and Narok (Figs. S4-5, S8; (31)).

Second, the most severe food competition between livestock and wildebeest should take place

during the dry season when the wildebeest reside in the Mara (34). Third, wet season

competition in NCA is further reduced due to the risk of transmission of malignant catarrhal

fever by calving wildebeest and the resultant avoidance of wildebeest calving sites by Maasai

pastoralists. Altogether, competition between wildebeest and livestock is highest in Narok and

lowest in NCA (35), suggesting the NCA boundary still functions as a soft boundary in contrast

to Narok. The observed squeeze thus occurs most strongly in the dry season, a pattern that is

supported by detailed surveys from Narok (Fig. 2). Wildebeest collar data show a (1)

displacement of wildlife away from the dry season range in Narok and towards Northern

Serengeti and the Western Corridor (Fig. S26; (31)), and (2) increasing wildebeest utilization in

the UPA Strong and UPA Medium (except for the first 7 km)(Fig. 4A-B).

5

Consequences for the ecological functioning of the CPA

In addition to the severe effects of human disturbance in the border regions of CPA, our data

suggest that these compression effects (Figs. 2-4) spatially cascade to modify ecosystem

processes over the entire CPA, not just the boundary. Grazing intensity (by wildlife) measured at

eight long-term grazing exclosure (LTGE) sites, each with three pairs of ungrazed (exclosures)

and control (unfenced) plots, across SNP (48 plots in total; Fig. S12; (31)) has increased by 16%

between 2001-2016 (ca. 1.1% per year (Fig. 5A, S28A; (31)). A Generalized Linear Model with

plot-pairs as subjects (blocks) and year and September-June rainfall as covariates, shows that this

change is not explained by rainfall (Table S7; (31)). Concurrently, the total area burned in the

CPA decreased from 55% to 34% without changes in fire management, while maxNDVI

decreased by 8% on average from 0.78 to 0.71 (Fig. 5B-C). Wildebeest formerly spent the

longest time on the Serengeti Plains, the Central Serengeti and parts of the Western Corridor

before moving to the Mara Triangle and returning through the area bordering the LGCA. In

recent years, the wildebeest distribution has extended farther south and west of the CPA into

areas that receive greater rainfall and feature high wet season biomass of plants living on poorer

quality soils (Fig. S26E, S28B). Increased use of such areas inside the CPA would be expected

when herbivores are displaced from preferred grazing sites in Narok and LGCA as they are the

only other areas with permanent water. These changes in wildebeest use, grazing intensities, area

burned and maxNDVI in the core ecosystem cannot be explained by changes in wildebeest

population numbers (Fig. S29; Table S8 (31)) or decreasing rainfall ((36); Fig. S30-S31; if

anything, there was a trend of increasing rainfall). Changes occurred simultaneously with the

increased human dominance outside the CPA and its boundary areas, and together provide strong

evidence that ecological function is changing at the core of an ecosystem due to compression of

wildlife.

It is unclear why this habitat compression has not resulted in an observable decline in wildebeest

numbers, since the overall abundance of wildebeest is thought to be regulated by dry season food

availability (34). It is possible that the trend of increasing rainfall (Figs. S30-S31; (31)) has

resulted in sufficient primary productivity to still support the current densities of wildebeest (Fig.

5A). Alternatively, the wildebeest population may not be near carrying capacity, or may not yet

have reached a new equilibrium (37). While the long-term population trend is relatively stable

and indicative of food limitation (Fig. S29), a large percentage of the population (up to 12% year-

1) is removed each year for bushmeat (38), and this offtake may dampen the role of food

competition in wildebeest mortality, and potentially compensate other demographic components

such as birth rates or juvenile survival. Overall, the future impacts of these changes in space use

on animal numbers are uncertain and of potential concern.

The park-wide increased grazing intensities are associated with a number of ecosystem function

changes. Data from the LTGE sites shows that plant biomass in grazed areas in the CPA

depended much less on annual rainfall in the period 2009-2016 than over the same range of

rainfall variation during the period 2001-2006 (GLM Year x Rainfall Interaction, X2=5.31,

P<0.03; Fig. 5A, Table S9) after accounting for the effect of grazing on biomass. Reduced

vegetation responsiveness suggests that increased grazing intensities inside the park may reduce

the resilience of plant productivity. Measurements of multi-year dynamics of soil organic carbon

(SOC, 0-30 cm depth) in grazed plots reveal a significant unimodal response to grazing intensity

(Fig. 5B), with negative changes at higher grazing intensities (GI>0.55). This response suggests

that the increased grazing intensities due to a “squeeze” effect decreases soil carbon

6

sequestration in Serengeti grasslands (39), which we see as a significant decline in the number of

plots that sequestered more than 1 Mg C/ha between 2009-2017 (6 of 21 plots, 28.3%) than

between 2001-2008 (14 of 24 plots, 58.6%)(X²=4.01, P=0.04).

Other data from the LTGE experiment suggest three different ecosystem responses that might

explain why compression and increased grazing intensity would yield lower resilience and

carbon storage. First, higher grazing intensities were significantly associated with higher percent

cover of largely unpalatable forbs and lower cover of known N-fixing species, including

legumes, in grazed plots (Fig. 5C)(40). Second, as indicated by a significant quadratic regression

model, higher grazing intensities shifted effects of grazers on root biomass significantly (P <

0.01) from positive to negative (Fig. 5D). Third, effects of grazers on production of hyphae by

arbuscular mycorrhizal fungi, important plant symbionts for phosphorus uptake, shifted from

positive to negative as grazing intensity increased (P<0.01; Fig. 5E)(41). These relationships

suggest that the higher grazing intensities associated with habitat compression may weaken

mutualistic relationships that assist nutrient acquisition (Fig. 5C,E) and increase belowground

carbon inputs (Fig. 5D,E). Furthermore, increases in unpalatable forbs are associated with lower

representation of dominant grass species, possibly further exacerbating the degradation of

primary productivity that supports the diverse and dominant food webs of the Greater Serengeti-

Mara Ecosystem (42). These changes may signal future degradation in CPA that has already

happened in human-dominated community areas.

The way ahead Today, wildlife competes with cattle for grass, generating a conflict in both UPAs where

aspirations to increase cattle grazing are restricted by competition with wildlife and in PAs when

cattle are moved into the park to compensate. While people were evicted from current CPAs in

the 20th century, wildlife is still allowed to roam the village lands, creating potential conflict

over this asymmetric historical relation. Our results illustrate that these conflicts at the periphery

of large PAs can have strong impacts on the ecological functioning at the core. These results

highlight the challenge in managing ecosystem edges for effective whole-ecosystem biodiversity

conservation, given the current rate of human population expansion and land-use change in its

surroundings.

As the GSME is among the largest PAs in Africa, the situation is likely to be considerably worse

for smaller areas. The GSME is one of the few, and perhaps most iconic ecosystems whose PA

boundaries were established based on ecological considerations of a larger landscape, intended to

encompass migratory animals (43). However, most other PAs across Africa represent now only

fragments of formerly much larger ecosystems (44). This landscape fragmentation has caused the

strong decline or extinction of most large-scale migrations worldwide (45). This calls for novel

strategies for improving the ecological integrity of fragmented ecosystems as well as for

preserving the last remaining places where these large-scale migrations still persist.

This will require re-thinking how to maintain the integrity of ecosystem edges, especially under

the rapidly increasing human densities and footprints in developing countries. For relatively

intact and contiguous ecosystems such as the GSME, sustainable long-term solutions are likely

to be found in ambitious land-use plans that actively manage resources beyond PA boundaries.

Strategies where humans and wildlife share landscapes under conditions established and

enforced by mutual agreement of local people and regional or national governments are likely

the way forward. People with rural livelihoods can strongly profit from nature, and nature can

profit from them. But only if neighboring communities are strongly involved in conservation

7

(46), preferably in long-term and locally-led programs with direct and long-term community

benefits from conservation actions (47) and conservation management has long-term stability.

This will require i) continued monitoring of both the ecological integrity and societal trends in

the surroundings of PA’s, ii) the building of more (justified) trust with local communities that

they will keep sharing in the benefits of natural resource conservation, and iii) ensuring that

livestock numbers, settlement and cropland expansion in the direct vicinity of core protected

areas do not go beyond a point where they impair the key structure and functioning of the

underlying socio-ecological system.

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Acknowledgements

Funding: This work is a product of the AfricanBioServices Project funded by the European

Union’s Horizon 2020 research and innovation program under grant agreement No 641918. The

study was also supported by the US NSF (DEB0842230 and DEB1557085) and by the German

Research Foundation (DFG # OG 83/1-1). Author contributions: MPV and HO conceived the

study. MPV, MER, JOO, JGCH, TAM and HO developed the concept. All authors contributed

data. MPV, AE, JOO, MER, CMB, JP, JGCH and TAM analyzed the data. MPV and MER wrote

the first draft of the manuscript and all authors contributed revisions. Competing interests:

Authors declare no competing interests. Data and materials availability: The data are located

on the Dryad Digital Repository. Interactive maps with GIS data access of several figures are

available at https://arcg.is/01CjXW

Supplementary Materials:

Materials and Methods

Figures S1-S31

Tables S1-S9

References (48-81)

11

Fig. 1. The concept of spatial compression in protected areas. Unsustainable activities outside

a soft-edge core protected area (CPA) resulting from human population growth spatially

compress wildlife, leading to more intense use of protected land and multiple possible

consequences for the magnitude and stability of ecosystem processes and services. Increased

human population, livestock densities and/or agricultural intensities convert soft borders that

effectively extend the CPA (left figure) into hard borders that effectively compress the CPA

(right figure). Lines represent hypothesized wildlife (blue) and livestock (red) densities and

agricultural intensity (green).

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Fig. 2. Spatial compression of burned area in the Greater Serengeti-Mara Ecosystem.

Different colors represent the last year each pixel burned between 2001 (blue) and 2016 (red)

visualized using the MODIS burned area product. Magnifications show the same map overlaid

with livestock paths (left) and bomas (right). Solid black lines represent borders of Core

Protected Areas (CPAs). Grey hatched areas are Protected Areas of Sustainable Resource Use

(PASRU) inhabited by people and grazed by livestock. The black dashed line is the boundary of

the Greater Serengeti-Mara Ecosystem that represents the area formerly used by the migratory

wildlife.

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Fig. 3. Spatial expansion of humans, livestock and the compression of wild herbivores over

multiple decades. Wildlife and livestock trends shown for both wet (top) and dry (bottom)

season. Density estimates are plotted against distance to the border of Masai Mara National

Reserve (MMNR) covering the first 15km inside the MMNR and 70km outside. Human

settlement, people and livestock densities increase through time close to the border and even

inside the MMNR. At the same time, wildlife densities decline, especially in the dry season, and

these effects stretch increasingly farther into the MMNR.

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15

Fig. 4. Changes in wildebeest occupancy, fire and vegetation greenness in the border

regions of the Core Protected Areas (CPAs). Wildebeest utilization between 1999-2007 and

2008-2017 (A, C), mean area burned between 2001-2005 and 2011-2016 (E), mean maxNDVI

between 2001-2005 and 2011-2016 (G) and the change between the two periods (B,D,F,H) as a

function of distance to the border for three different border types between CPA and: 1) Protected

Area with Sustainable Resource Use (PASRU) with medium border control against illegal

activities (PASRU medium, blue line), 2) unprotected areas (UPA) with strong border control

(UPA strong, red line), 3) UPA with medium border control (UPA medium, orange line). Panel

C and D show the same information as the PASRU (blue lines) in panel A and B but now split up

for the three different PASRU areas. Black line represents the overall weighted mean. Data

covers both the Tanzanian and Kenyan side of the ecosystem.

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Fig. 5. Changes in grazing intensity, burned area and maxNDVI between 2001 and 2016 for

the entire area designated as Core Protected Area. A) Grazing intensity (GI; mean ± SE),

measured through herbivore exclosures, increases by 1.08% per year on average. B) Area burned

decreased by 40% in 16 years time (solid red line). C) MaxNDVI decreased by 8% in 16 years

time. The burned area and maxNDVI increased in 2016 (red triangle) due to management actions

in eastern Serengeti National Park. Excluding this data point results in a stronger correlation and

more explained variation (dashed red lines; Area burned=0.53-0.017*years, R²=0.38, P=0.01;

maxNDVI=0.77-0.047*years, R²=0.33, P=0.03).

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Fig. 6. Consequences of increased grazing for ecosystem processes. Data from 2001-2017 in

the Serengeti Long-Term Grazing Exclosure experiment (LTGE; 8 sites with three exclosure-

control plot pairs, N = 24). Linear models with quadratic functions contain significant

coefficients (P<0.01), and fit significantly better than straight lines (R2 improvements > 0.2).

Vertical dashed lines represent mean grazing intensity across all sites in 2001-2008 (blue) and

2009-2016 (red). A) Residual aboveground biomass averaged across grazed plots at each site

after accounting for the influence of grazing intensity in a GLM, exhibits significant (P<0.01)

relationships with CHIRPS satellite-estimated rainfall across 8 sites in 2001, 2002, and 2006

(blue points, N=21), at 7 sites in 2009 and 6 sites in 2016 (red points, N=13). Slopes are

significantly different (P<0.04). B) Changes in soil organic carbon (SOC) in each grazed plot

from 2001 to 2008 (blue circles, N=24) and 2009 to 2017 (red circles, N=21). C-E) Effects of

excluding herbivores in plot pairs (control–exclosure measure) at different mean grazing

intensities (measured in 2006 and 2009) on C) percent cover of N-fixing plants, both grasses and

legumes (open circles) and low palatability forb species (solid circles), D) root biomass and E)

production of hyphae of arbuscular mycorrhizal (AM) fungi.

Submitted Manuscript: Confidential

18

Supplementary Materials for 5

The Serengeti squeeze: cross-boundary human impacts compromise an iconic

protected ecosystem

Michiel P. Veldhuis*, Mark E. Ritchie, Joseph O. Ogutu, Thomas A. Morrison, Colin M. Beale,

Anna Estes, William Mwakilema, Gordon O. Ojwang, Catherine L. Parr, James Probert, Patrick

W. Wargute, J. Grant C. Hopcraft and Han Olff 10

Correspondence to: m.p.veldhuis@rug.nl

This PDF file includes:

15

Supplementary Text

Figs. S1 to S31

Tables S1 to S9

20